A very rare hierarchical SB4 system detected in the Gaia-ESO Survey?.

The Gaia-ESO survey (GES) is a ground-based large spectroscopic survey targeting a hundred thousand stars for which radial velocities, atmospheric parameters and detailed chemical abundances are released. The bright A2V star HD 74438 has been detected with four radial velocity components in its cross-correlation function. This star belongs to the young open cluster IC 2391 and was already suspected to be a triple system because lying 0.9 mag above the main-sequence in the colour-magnitude diagram of this cluster. The GES spectra have revealed the physical nature of two pairs but the time coverage was insufficient to derive the orbital parameters. On-going follow-up of this star with the HRS/SALT and HERCULES/MJUO allows us to derive an orbital solution of the faintest SB2 (P = 4.4 d, e = 0.16). The orbital elements of the brightest SB2 are more difficult to assess possibly due to the interaction of the faintest SB2 and preliminary solution gives P = 20.5 d and e = 0.36. The long-term variation seems to show that the two SB2 are gravitationally bound.